It is conventional to provide oil ring assemblies for internal combustion engines with two oil rails that are yieldingly urged radially outwardly into contact with the cylinder wall of an engine by a piston ring spacer/expander. It has been found by extensive testing that there is a tendency for the oil rings to move circumferentially so that the oil ring gaps align with each other and frequently with the gap of the spacer/expander. In such an occurrence, oil consumption of the engine is substantially increased.
Past history has proven that there is a detriment to oil economy when the gaps of the two rails align circumferentially. The magnitude of this detriment has been measured in the range of 40% reduction in oil economy.
There is, therefore, a need to lock the rotation of each rail relative to the expander in an installed staggered circumferential orientation. Prior art to accomplish this desired goal is represented in U.S. Pat. No. 4,572,520. In this patent, two potential locking methodologies are presented. One presents an axial displacement of rail material to engage with the expander. This methodology, although effective, results in "directional" rails which must be oriented, whereby, the axial displacement of the top rail must be installed downward to engage the expander and the axial displacement of the bottom rail must be installed upward to also engage the expander. The second methodology presented in U.S. Pat. No. 4,572,520 presents a rivet feature which protrudes axially from the rail in both directions. This feature is "nondirectional"; however, the presence of the axial displacement on the rail towards the groove side requires the presence of a relief into the groove to accept the rivet head, as well as the need to orient the rail upon assembly, whereby the rivet head is circumferentially aligned with the groove relief. Additionally, this method results in the locking of rail rotation relative to the piston. Both methods require the proper orientation of the rail relative to the expander prior to the installation of the rail with the expander. These directional and/or circumferential orientation features present major inconvenience to the automated loading and circumferential staggering of the oil ring components.
Prior art to accomplish component circumferential staggering of gaps for multiple piece compression ring assemblies exists as demonstrated in U.S. Pat. No. 3,391,942. In this patent, an expander ring is bent to form ribs that engage recesses on compression rings. Due to the multitude of components, with dimension stackups and the associated degree of difficulty in loading said components into compression groove, the assembly is economically prohibitive.
Other oil ring patents exist (U.S. Pat. Nos. 3,184,245, 3,346,252 and 3,105,695) which exhibit locking mechanisms to lock the rotation of the expander relative to the piston but do not restrict the rotation of the rails relative to the expander.
Among the objectives of the present invention are to provide an oil ring assembly which obviates the aforementioned problems; which can be achieved at relatively low cost; which can be assembled readily without any possibility of misassembly; and which would be effective to eliminate any possibility of alignment of the gaps of the oil ring rails and the spacer/expander.
An oil ring assembly embodying the invention comprises a pair of split rails and a piston ring spacer and expander on which said rails are mounted. Each rail is provided with a radially inwardly extending protrusion that lies substantially entirely within the thickness of the rail. The protrusion extends into and engages the spacer expander to limit the circumferential movement of the rail relative to the spacer/expander.
A feature of the present invention is the fact that the locking force (to prohibit rotation of the rails independently relative to the expander) is energized by the tension generated by the expander upon compression of the assembly to bore diameter. This feature permits the ability to stagger the relative orientation of the expander and the rails after installation of the components into the oil ring groove but prior to compression of the assembly to bore diameter. This feature is important since some automated ring installation equipment installs the rails onto the piston groove aligned with each other and subsequent circumferential staggering is required and not possible with oil ring prior art U.S. Pat. No. 4,572,520.
Another feature of the radial protrusion on the invention is that the rail is functionally axially nondirectional and no efforts must be expended to orient the rail's bump side up or bump side down as contrasted with the axial locking feature in the prior art U.S. Pat. No. 4,572,520.
Another feature of the radial protrusion in this invention is that the rail incorporating this invention is compatible with any spacer/expander in which the circumferential gap between expander rail support contact pads is greater than or equal to the circumferential length of the radial protrusion on the rail. For example purposes only, the described expander per FIG. 1 shall be utilized in describing the invention.